Re: DLL Load issue

From:

"Alexander Nickolov" <agnickolov@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Tue, 4 Sep 2007 11:23:19 -0700

Message-ID:

<#M5FhCy7HHA.1484@TK2MSFTNGP06.phx.gbl>

You can share _data_, not an object. This is mostly irrelevant
to COM as it deal with basic IPC (inter-process comminucation).
Your options are a shared global data segment in the DLL and
a memory mapped file. The latter is much more flexible and
I'd always go with it. And don't forget you need named mutexes
for data synchronization...

--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov@mvps.org
MVP VC FAQ: http://vcfaq.mvps.org
=====================================

"George" <George@discussions.microsoft.com> wrote in message
news:3CAE85A3-B869-48EA-81A2-19054FEB75A6@microsoft.com...

Thanks Alexander,

I have the requirement of building an DLL other than an EXE. Are there any
solution to make a COM DLL share data (single copy) among different
processes
which utilizes the object?

regards,
George

"Alexander Nickolov" wrote:

Then read Brian's response about COM+. Alternatively,
you can convert your DLL into an EXE COM server.

--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov@mvps.org
MVP VC FAQ: http://vcfaq.mvps.org
=====================================

"George" <George@discussions.microsoft.com> wrote in message
news:A171CB08-6EFD-41BA-94B4-ACB0E31B5E16@microsoft.com...

Thanks Alexander,

I am developing a COM DLL using native unmanaged C++. I want to let all
applications which utilizes the CoClass of the DLL share a single copy
of
object instance (other than each application process have a separate
copy
of
object instance). Do you think it is implementable? Any reference
materials
to learn or comments?

regards,
George

"Alexander Nickolov" wrote:

Actually, a DLL can be loaded in a process muiltiple times,
just not simultaneously. Once you unload a DLL you can load
it again into the same process. Of course the DLL's importlib
must not be linked to other images in the same process (the
executable image or that of any other DLLs loaded in the process)
or else you won't be able to unload the DLL in the first place...

--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov@mvps.org
MVP VC FAQ: http://vcfaq.mvps.org
=====================================

"Igor Tandetnik" <itandetnik@mvps.org> wrote in message
news:eDU46ux6HHA.4436@TK2MSFTNGP03.phx.gbl...

George <George@discussions.microsoft.com> wrote:

I am developing a DLL and I implement a class in the DLL. I am
wondering in the two situations,

1. DLL is loaded by a single process multiple times

This cannot happen. If you attempt to load a DLL a second time, its
reference count is simply incremented.

2. DLL is loaded a couple of times by multiple process

How much times will the constructor be invoked?

As many times as an instance of the class is created. The number of
times
the DLL is loaded is irrelevant, unless you have a global instance
of
the
object. In which case, the constructor of each such object will run
once
every time a process loads the DLL.

I want to learn how
objects inside a DLL is shared between different process.

They aren't.

Is it
possible to make multiple process share one single class (class is
defined in DLL) object instance?

Not really. You can share simple data (fundamental types like
integers
or
doubles, and arrays and structs thereof). See

http://support.microsoft.com/kb/125677

--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going
to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925